The long term objective of this research is to find methods to prevent senile macular degeneration (SMD) and to arrest the progression of existing SMD. The specific aim of this research is to complete a pilot investigation of the role of selenium nutrition in SMD and to determine if selenium supplementation is a candidate method for reducing the progression of SMD. This pilot project is intended to be preliminary to a larger scale study of selenium and SMD which may lead to a clinical trial. We have found that the degree of human SMD severity is inversely correlated with the level of glutathione peroxidase (GSH-Px) enzyme in the plasma. GSH-Px is a selenium dependent enzyme and lowering dietary selenium below a certain level leads to a linear decline in plasma GSH-Px activity in humans. The plasma GSH-Px level appears to saturate above this level of dietary selenium. However, whole blood selenium is approximately linearly related to the dietary selenium to levels far above the saturation of GSH-Px activity. We will measure whole blood selenium levels using wet ashing and a high pressure liquid chromatography method in the present pilot study. Parallelism of whole blood selenium and plasma GSH-Px is strong evidence that low levels of plasma GSH-Px are due to inadequate selenium nutrition or absorption. Selenium supplementation would then be indicated for future studies. In future studies the response to selenium supplementation will be monitored both in selenium status and SMD progression. High levels of dietary selenium can be toxic but not if the selenium is poorly absorbed and so poor absorbers may be given unusually elevated dietary levels. The proposed study should be capable of determining the need for a large scale exploration of selenium and SMD.